It has previously been known that it is possible to determine the state of deterioration of a catalytic converter by sensing parameters both before and after the catalytic converter along the exhaust path of the motor vehicle engine. The sensed values can be compared with idealized values to determine whether the sensed converter efficiency meets a predetermined standard. In such systems, air fuel sensors, often referred to as universal exhaust gas oxygen sensors (UEGO), as well as heated exhaust gas oxygen sensors (HEGO), may be used to detect the degree of catalytic converter efficiency. However, the previously known systems involve algorithms that respond to sensor inputs by reliance upon laws of physics and chemistry to calculate or model the converter activity.
Regardless of the types of sensors used in sensing components of the exhaust stream, the catalytic converters and sensors are subjected to harsh conditions which can substantially affect the working life of both and interfere with the acquisition of accurate data. Moreover, repeated cycling of heating and cooling of the internal combustion engine accelerates deterioration of the powertrain and monitoring system components. Moreover, since the sensors are subjected to a wide variety of exhaust flow conditions under the various operating conditions to which the vehicle is subjected, the information obtained from the sensors must be monitored and compared in a manner consistent with the complex variety of operating conditions to which the sensors are subjected. Accordingly, the previously known monitoring systems usually acquire data for comparison only at steady state operation of the engine.
An example of previously known attempts to monitor convertor activity by simulating the time dependent performance of an exhaust gas catalyzer is disclosed in U.S. Pat. No. 5,214,915. An air mass flow to the engine is measured and the oxygen flow represented by the air mass flow is computed. Then the deviation .DELTA..lambda. is determined by a model with respect to the time-dependent performance of oxygen partial flows and inputting the oxygen storage capacity of the catalyzer and computing the time-dependent trace of the .lambda. value at the outlet of the catalyzer. The quantity of oxygen which the catalyzer can store at saturated state is dependent upon its performance loss and the partial pressure of the oxygen. Nevertheless, a forward .lambda. probe is mounted in the inlet pipe of the catalyzer to measure the .lambda. value while further .lambda. probe is mounted rearward of the catalyzer in the outlet pipe to measure a .lambda. value. However, with the previously known sensor-based systems, the system provides best results when steady state engine operating conditions are examined for comparison with desired performance standards.